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Glyphosate-resistant palmer amaranth was identified in seven west Texas High Plains counties along the New Mexico border last cotton growing season, up from one county the year before, reports Texas A&M AgriLife Extension Service weed specialist Paul Baumann.

Baumann said this rapid spread in west Texas is mirrored by a large area in central Texas stretching from Hill and Ellis counties to the upper Texas Gulf Coast through southeast Texas where glyphosate-resistant common water hemp or careless weed has been identified.

Baumann reported on these two “alarming” issues at the recent Beltwide Cotton Conference in San Antonio, where he told growers and others that the “horror stories” of pigweed resistance need not be repeated in Texas with a proactive approach to weed management.

Glyphosate-resistance is showing up in Roundup Ready crops where certain biotypes are resistant to the herbicide. Careless weed resistance was first identified in 2005 with spotty infestations along the Gulf Coast, and then it was hit or miss until 2010, with it occurring in other sites, he said.

“If all else is killed out but that one plant is different, that is the start of the problem,” he said. However, it may not be a particularly new problem by the time it becomes visually obvious.

“A grower could treat herbicide resistant plants several times before he realizes they are not dying because of resistance. Making the problem worse is that pigweed can shed 400,000 or more seeds.

“So if that one weed is not killed, then later that year or the following year, there may be a whole patch of this resistant biotype of the weed.”

Glyphosate-resistant Palmer amaranth was first confirmed in Terry county a year ago. Last season it was identified in surrounding counties — Hale, Hockley and Bailey.